Vulcanization of rubber



' such 7 as 2 mercapto-benzothiaZole.

Patented Aug. 10, 1943 UNITED *s'mrss mass; orricli;

55 ,t 1 mosNrzs'rroNor Rosana f Arthur M. Neal, Wilmington', l el. andBernard r M. Sturgis, Pitman,-N;-J., assig n ijs toE. I. an I Pont deNemours &,Compa'n' Del a corporation of Delaware No Drawing.

This invention relates to the acceleration of the vulcanization ofrubber and more particularly to the use of Z-merc'apto-thiazoline forsuch purpose in conjunction with certain compounds as activatorstherefor. q i

Z-mercapto-thiazcline and some of its deriVa-- tives have been proposedas accelerators for the vulcanization of rubber. However, suchmercapto-thiazolines were found to be very weak andinefiectiveaccelerators so that they have not 10 been employed commercially untilthe present time. 2-mercapto-thiazoline and its hom'ologues are acidiccompounds. This is show'nfby the fact that they are readily soluble incold dilute solutions of caustic alkalies and may be precipitatedunchanged from-these solutions by the addition' of acid. Iheyalsolreadily form salts with amines and other basic'substances and, ingeneral, exhibit the reactions of acidic compounds. i

It is known that the cures, obtainable by many basic and neutral-organicaccelerators, such as metaphenylene diamine and urea, can be improved bythe addition of small amounts of vari ous organic acids which activatesuch accelera i tors. 467,197 to W F. Russell. It is also well knownthat acidic accelerators of vulcanization, such as 2-mercapto-benzothiazole, behave in an entirely difierent manner. Morton-, inPatent, 1,929,561,

discloses: that; aromatic carboxylic acids iretard ratherQ-thaniactivate .such acidic accelerators, Thies',iin, Patent2,058,840,- and Ca'dwell, in Patent 1,871,037, disclose thataliphatic'fcarboxylic acids retard, ratherlthan activate, acidicaccelerators;

thereioregbeg expected that, the organicfcarbox-j ylic acids would also,retard, rather than activate,

v the, zem'ercapto thiazolineaccelerators.

it is'anfobj'ejct ofithe presentinvention to previde a new andimproved'methodofvulcanizing' 4O rubber ,to obtain vulcanized rubber trimproved properties. Another object is to "convert2i-mercapto-thiazolineirom relatively weak accelera 5 Application November Serial No. stages22 Claims. (craw -7 5 This is particularly shown in-Patent 1-, '25

It would,

tors of commercial valueto strong wacjcelerav t o afes ,mmi' e i l I vaue uri rr f. Ijectis torimprove thegvulcar i atipa qrgr bpejmy empibymgthe n new combinations of 2 -"m efr-' captoathiaiolirief iaccelerators} with certain care 'b o X ylic' iacids wh ch activate thej'accelerators to,

rea er, ithemfveryg active at-Ii'orinal yulca'nizing temperatureswhilemaintainingIthemfsufiiciently inactiveatflprocess'ing,temperatures'for com-Q rnercial utilization;A-s'till'iurtheriobject is'to' provide new [combinations 5 ofaccelerators and acceleratoractivators which willproducejvulcaniZeclrubber ofim'proved properties; Qther objects are to, provide newcompositions of matter and to advance the art. {Still othenobjects willappear hereinafter. f 5

v i T e. above and'o'ther" objects mail be accorn f plishedin accordance1 with, our invention, which comprises incorporating; in'ia rubber mix,a small proportion .of a vulcanization acceleratorv of: the a class 1 of2,-'m8rcapto-thiazoli'ne, C-alkyl'. 2;mer-l capto-thiaz'olines, C.-hydroxyalkyl -.2- merc-apto-; thiazolines"and-saltsjofj such2-mercaptothiazol inesiandga small proportion '.of an activator for suchaccelerators which activator is selected from th'elclassi ofunsubstituted jaroma'tic mono- .carboxylic acids, unsubstituted aromaticdic'arej boxylilcjvacid s, sulfur-free aromatic monocarbom' ylicj acids]containing one non -hydrocarbon, 'substituent, and anhydrides of suchacids; either i ith i w he a sm por on Man 111 substitutedaliphaticmonocarboxylic a'cidoiffrom Y 10 t'o 20'-carbori atoms. Wehave'foundjthat the 2-mercapto-thiaz'oline accelerators act in" the,

presence of such carboxylic acids and theiranhyfdrides in a mannerdistinctly-different from the 'thiazoles andother acidic accelerators.-Whi1e such carboxylic acids retard-the action of thiazoles and similar.acidicacceleratora'tl'ieyhave a tremendous activatingefiecton the 2-mercaptothiazolines of our invention. f In the absence of an acid; the2+mercapto thiazolines produce such poor cures that thel'resultingvulcaniaates are ofr thiazoline acceleratorsgive vulcanizates of highmoduli and tensile strength which are extremely V Cuminic acid valuablecommercially, r The 2-mercapto-thiazoline accelerators, which V Benzoicanhydrideareto be employed in accordance with our invention, are2-mercapto-thiazo1ine, the C-alkyl 2-mercapto-thiazolines, theC-hydroxyalkyl 2- mercapto-thiazoiines and thesalts thereof. vThe 1Qnumbering of the Z-mercapto-thiazoline ring is v as follows:

'7 I a a 0 003 Z o-Toluic'acid C-SH 5 2 V CH3 HCS I In 1 By the term"C-alkyl 2 l-mercapto thiaz'olines,' we mean 2-mercapto-thiazoline inwhich one or more of thehydrogen atoms'in the '4 and 5 posi termC-hydroxyalkyl 2-mercaptothiazo1ines,-

we mean that one or moreo'f -the' hydrogerisin gb?" the 4 and 5positions have beensubstituted 'by hydroxyalkylgroups and the'otherhydrog'ens inthe 4 and 5 positions are either present or are 7substituted by 1 or more a'iiiyi gioups." "By';the-1- term alkyl, wemean an aliphatic hydrocarbon radical. By the term hydroxyalkyl,weflme'an an aliphatic hydrocarbon ,radicalin which one hydrogen hasbe'rf repiace'd -iiyja hydroxy 'g'roupi Such t 2-Tnercapto=tl:iia'zolineaccelerators afre tions 61'. carboxylic acicis' orj our mventiom.me'aierna te arboxyiieacfds-orohrmventmn are the-unsubstitutearomaticfinonocarboxylib acids," we un s-assumed Ifaromaticdicarbbfxyiic acius msuirumiee'ar matie -monocarboxyiic f acidscdmmne'onenon hydiobarbon substi'te uent anaemiyarrdtsidf such?acidsffWhen'we refer toe'zrboxyneacids herein' and in 'tlieclaimsi we}mean tne 'fre 'alcid's as-cisunguisnewrrom for the oxygen of thecarboitYFg'iUiips', consist of icarldori 'andhydrogenffdiyari'aromatieaeid,

uiariyi tliif'unsdbstitiitefl faromatic monocarbozi; y1i 'c acids; fth'e5ai'ofri'af earbqxyue 'acidgfof our invention, is;renewingtriave'iieenfounmo L; l ara-anisio acid;

h I tors cfourfi'nyentiqngiwe'gen (so eran'prererthe-unsubstitutedaerusanavomtm: r x p I H ticula'rly ii'esirable"results' are obtained whentions are substituted by aIkylQgrOtip i BbIPeta-maphthmc acld [ID-coon OOOH {'"V ihilethe'aromatic' caj'rlaoizyiicacids of our in:- VGfIfi OII may beferhpldyed aione as activators withsatisfactory results; have found thatfpa'raliphati f"monocarboxylic.acids containing:- from in' the ,pt'esence or zsucif aliphatic acids;smaller 7 ounted?t i'a b t r b illi f ni si ay be employed .to 'obtainastrong. a ctiyating'jieffeot. By the teifm' unsubstituted"faliphaticmonocar boxylic facids, we. .mean [to include only those acids jWhi'ch,"eXc'ept :forfthe oxygen, of the car- 'bpxyls'group; consist Qf :carbon"and hyd ogen. Of such acids, we have found 'stearic', .acid and olei' c"acid to be particularly satisfactory.

ete

The aromatic carboxylic acid and anhydrides of our invention willgenerally be employed in a the proportion of from about 0.05 part toabout parts for each part of the Z-mercapto-thiazdline accelerator. Wepreferably employ from about 0.5 to about 3 parts of the aromatic acidor anhydride for each part of the accelerator. When an aliphatic acid ofour invention is employed, it will generally be desirable to employ itin the proportion of from about 0.5 to about;

10 parts for each part of th 2-mercapto-thiazolin accelerator, togetherwith from about 0.05 a

to about 4 parts of aromatic acid or 'anhydride;

Preferably, we employ from about 1 to about 5 I 1 parts of the aliphaticacid and from about;0.1-

to about 2.5 parts of aromatic acid-oranhydride for each, part of2+mercapto-thia'z 0line acceler- MI d cure, obtainable jwith 2-mercaptothiazoline. and Z-mercapto benzothiazolefin the absence of an acidicsubstance, the following stocks werc'jprepared",

Stock A B Smoked sheets. 100 Zinc oxida. Sulfur 3 Z-mercaptothrazolme.2-mercaptobenzothiazole Results ofte'sts on these stocks aeseaf'in TableI.

' It can be seen, from these tests, that there is a marked difierence incure between stock A, containing 2-Inercapt0-thiazoline, and stockB,containing 2 mercapto benzothiazole. T h e moduliand tensiles, producedby the Z-mercatptothiazoline, are so low that the stock may be said;

to be very much undercured and is useless for commercial purposes. Onthe other hand, Z-mer: capto-benzothiazole produces good 'moduli andtensiles and gives commercially important vulcanizates.

Since both of these accelerators, used in the above examples,- areacidic accelerators, their great difference in behavior, when'usedincorn-V. bination with an aromaticlcarboxylic acid, or

is very surprising. 2-mercapto-benzothiazole is very much retarded,especially in the shorter,

cures, as is indicated by the prior art. Z-m'ercapto-thiazoline, on theother hand, istrern'en t illustrate the as? difieren'ce in derivatives,as all other acidic accelerators tested,

aromatic carboxylic acids on 2-m'ercapto-benZothiazole thefollowingstoolrs wereprepared: 1

Stock to 2-mercapto thiaaoline, its homologues'and its 7 such, as2-mercapto benzothiazole,its salts and"; organic derivatives, and'dithio'carb'amic acids and their derivatives, were retarded and gave Alower moduli andtensiles, at'least'intheshorter In order to illustratethe retardingaotion'of sheetsl Zinc oxide.

' Smoked These stocks were yu'l'caniaed 'forperiods or "20 I and 30rninutes at 274 amines thejmoglulus of these tests are presented irra'lable 11,1:

"1 1 blestockf Stock K C v D1- Templ 7 H I 1 cured 'Modulus at 600%elongation,

I 7 lbsl/sqJn.

Min. cured 'l en sile at brealgllbs/sq. in.

2,375; 1,725 2, soc 2,150

In Table 11, it can be seen that an o f the acids .and anhydrideslowered the moduli and tensiles given by Z-mercapto-benzothiazole alonein stock B; Thus, whi1e the prior .art indicates that acr (59 tested: Y

acid anhydride in accordance with our invention, r i I dously activatedby the aromatic carboxylic acids of our invention, and is therebytransformed from an accelerator of no importance to one of the mostthiazole in modulus and tensile characteristics,

desirable accelerators of vulcanization known today. =It evenexceeds'2-1nercapto-benzowhile retaining good processing safetyff Thisability to be, so activated, with aromatic carboxylic acids and acidanhydrides, seems-peculiar i Cuminic acid. 5

tain acidic substances: increase the processing safety of stockscontaining z-mercapto-b enzothiazole by retarding the cure at processingtemperatures, it isplainly seen that this retardation 1 of cure alsotakes place 7 I 1; higher vulcanizingtemperatura'where it is veryundesirable.

- This retardation of the Y rate ofvulcanization f by aromaticcarboxylic acids and'acidanhydrides' is d, to Z-niercapto-benzothiazole;but I l is 5 Present when derivatives'of'2-merc t i benzothiazole areused, and even with other typesof acidic accelerators such 'asfd'ithidcarbamates' and dithioacids. This is illustra'tedbythe data givenin Tablev III. The followingstockswere Stool;

Benzoyliderivativo 2- mercapto-benzothia- 1 1 1 .Zinc s 2-rnerbenzothiazola Zinc hexamethyle thiocarbamate' Benzoicacidl';

and tensile figures were determine The results TabZQIIL. 7

V v stoekfl JStock' smci: shin 2. Stock" Stock "sto k curedcur'ed I vModulus at600% elongation, lbs/sq. in.

Tensile atbreakJbSJsqJin.

This retardationof the cure, which results when aromatic carboxylic;acids and acidan hydridesare employed with most acidic accelerators doesnot :take' place when 25mercapt0-thiazoline,

a homologue or a derivative thereof, is employed 7 as theaccelerator. Onthe contrary, 2-n1ercaptothiazcline, hcmo'logues" andderivatives are:greatly activated at ordinaryfcuring'temperature's by. aromaticcarboxylic acids-and acid 'anhydrides employed-"in accordance with ourinvention. Thus a. fasjg high modulus cure, so

over ithoseigivenihy, .stoclsfA. .,In.,fact, ftensile figures of over4000 lbsp/sq. in. wereproduced:

These activated stocks. give verydesirable cures,"

and are, at. the same time quite safe at processing temperatures, .as isindicatedby the filliminute curesat 1227" F. .Itica'n. beseen that,while a stock containing a Z-mercapto-thiazoline alone. (stock A) isvery much inferior to a stock' containing Lmercapto-benzothiazole (stockB),

' when the z-me'rcapto-thia-zoline stock is activated desirable in therubber industry, is produced.

This activatingefiectisdllustrated by tests car- .acrl Beta-naphth'oicCumimc @c d Para-anisic acid Bonzoic anhydri These stockswerevulcanizedandIthe modulus and tensile figures, determined-t These are"given with an aromatic carboxylioac'id or acidanhy- 'd'ride of ourinvention, it becomes vastly superior to v the 2-mercapto-benzothiazole' stock. This tremendous activation of an acidiclacceleratorof. vulcanization by aromatic acids and acid anhydrides is entirely newand ,unexpectedr Not only' are the aromatic carboxylic. acids and acidanhydrides of our invention individually useful as activators forZ-mer-capto-thiazoline accelerators, but theyareg-also. useful incombination with each other andwith other organic acids,

, particularly the unsubstituted aliphatic: monocarb ox'ylic acidscontainingJ-rom 10 to 20 carbon atoms. Stearic acid, as .well' as othersimilar acids, derived from fats andoils, such as palmitic and oleicacids, have long been used as rubber.

compounding ingredients with neutral or basic accelerators. Russell, inU. :8. Patent 1,467,197, claims beneficial action of these acidsdue totheir ability to solubilize zinc oxide.

Although a smaller amount of Z-mercaptO-Q thiazoline was used in thestocks N to R than" in stocklA, the Presence of the acids and anhydridesof our invention soactivatedit that the'modulus in b -11V, We have .nowfound that very beneficial and Table-JV v Stock' Stock Stock Stock stockStock 'Stock Min. Temp. .1 A M'; 1 N1 0 P Q. R cumd' m j t v 1 Modulusat6O0 %el0ngati0n,lbs1/sq. in.

Tensile at break, lbs/sq. 00 227 ,7 800 1,725 7 375 1,775 400 450 30 v274 875 s, 450 s, 550 3, 300 3, 575 2, 800, 3, 400

7 1N0 cure.

entirely unexpected'results are obtained-when a mall aniount of anaromatic carboxylic acid or acid anhydride of'our invention is added toa rubber. stock, accelerated with a 2-mercaptoand'tensile figures vvereincreased many times thiazoline and containing theamoun't, of steariction of acids, is not merely additive. The Presence: of even a smallamount of an'aromatic car-f In order to. show that'other aliphaticmono-j carhoxylic. acids, c-ontainingfrom lfl'to 2Q-carbonf atoms, areaiso operative accordingto our in'ven tion,stocks BB and CQwere preparedinwhidh boxylic acid or acid anhydride seems to exert a 5 cleic acid wasused intplace of stearic acid. strong activating effect on'the'2-mercapto-thi- 't I azoline in the presence of a long chain aliphaticStock monocarboxylic acid, such 'as stearicacid, that V is entirely outof proportion to the amount of 7' BB aromatic acid used. The addition ofeven 0.3 10 p p part of an aromatic acid or acid anhydride of g okeqsheetsn 100] 100 our invention often increasesthe modulus of the fi gistock as much as'60'-70%. This remarkable acti- 9101c acid 1 vatingeffect is illustrated in Table V which gives f,i,,%g, 3;; the results oftests on the following rubber stocks.

Stock s '1 11 -v w X Y 2 AA 100 100 100 100 a 100 1o, 10 10 a. 10 1o2-mercapto-thiazoline 0. 0. O, 0. 0. Benzoic acid Ortho-toluic acidGuminic acid Para-anisic acid Beta-naphthoic acid Alpha-naphthoic acidSalicylic acid. Benzoic anhydride.

These stocks were cured'forperiods of 30, 60 and 90 minutes at 274 F.and the resultingvulcanizates tested with the followin results.

Table V 1 7 Min. Temp. Stock Stock Stock Stock Stock Stock Stock StockStockcured cured S T U V W X Y Z 1 AA Modulus at 600% elongation,lbs/sq. in 1 F. V 3 3 30 27-1 1, 150 1, 475 1, 800 l, 450 1, 450 1, 5751, 425 1, 250 V 1, 275-- 60 274 1, 300 2, 400 V 2, 250 1, 975 2, 025 2,075 1, 725 1, 950 l, 750 90 274 1, 675 2, 525 2, 300 2, 250 2, 150 2,325 2,125 2, 350 2,025

Tensileat b eak, lbs.lsq. in.

It can be seen from these results that even very small amounts of thearomatic carbcxylic acids and acid anhydrides of our invention con-'siderably increased the moduli of the stocks. This 7 Q i is veryremarkable since'increasingthe' stearic acid content of stock S from 2%to 3% gives only about a 5% to 10% increase inmodulu's.

This is shown by the following results in which the 600% modulus ofstock Sis compared'with This activation of Z-mercapto-thiazoline bysmall amounts of aromatic acids and anhydrides, in the presence ofste'aric acid or other similar acid, is also present in the shortercures. The activation at processing temperatures is slight, however, andthe stocks retain their processing safety. r

Test results on these stocks are presentedqin' Table VI.

Table VI I; Modulus at M Tensile at I 7 @600? elonga-- break, lbs/ sq.Mm. Temp $1011 bs,/sq. 11.1. p 111." cured cured V 0 Stock Stock StockStock BB CC BB 7 CC Activation occurs on even "the short cures at 274F., but practically no activation is apparent 7 at 227 'F., so the stockretain processing safety.

anhydride in ,the presence of 'stearicac'id, also Beuzoic acid thiazjgilboth l he st cksaiiastacks-h: tainin'g caitbcn Black; 1 I;

manlfestsiits lf infa' rubber! stock, mitammgcabon bl'ackfl This isillustratedini'TableV11} a Stock DD EE Smoked sheets 100 Zinc oxide; 7"10 Channel black 25 Su1fur 3 Li Stearic acid- 1 2' 2-mercapto-thmz0line.- 0. 85

Table VII V V Ortllo-tliiica Modulus at ""Tensile'at 7 Table IX6007e1onga- 2 break, Min Temp tion,1$)s./sq. in. Ibs./sq.in. M T St k StSt k St k St k st k in. 6111131" no 0c 0c 0c 0c 0c cured cured curedcured JJ KK LL:

MM NN .200

Modulus at 600% elongationflhsz/sqf j I; i OF p V e0 2277 1,125 1150--1,00-1225 20 274 2,225 21350-1325 3,'550 7 7 3 1 50 274 3,000 3,225-4,525- i550 g 4 V1.75. 274 3,775 4,150- 4,925 4, 50 4 7 .5 274 4,0004,300 4,600 4,000

The use of aromatic acidsjincr'eases themcdu mercapto thiazoles but alsewithother-typeset we lus throughout the range of"curewlthout"" m: g"acidic -accelerators"finchay dit-hiocarbamates. pairing the processingsafety. 0 The following test' cnith zlrrc'isaltpfihcxambthyl Not only isZ-mercapto-thiazoline activated by ene dithiocatbamieslaeidailliistiiatedsthis-m a small amount of an aromatic acid or acidan- I i hydride in the presence of an acid such as stearic St ck acid,butits homologues and deriv atiyesarelilge- 35. i H I O wise activated.To illustratethisfact, the fol- V p p K lowing stocks were prepared: I i

4-methyl-Z-mercaptothiazoline I I Stock Zinc salt of2-mercaptothiazoline 0.85 Benzoic acid 0.3

Results of tests on r the. stocks care given :iin' 50 Table VIII, Min.cllfen-- stoclg PPv-stoclg-QQ T GW 11,225- 1,075?

1350' 1,125 Modulusat Modulusat; 55 i w 3 .1 a. i 000% elo'nga- J700%e1on a .:-It can 'bejseen, f-ro ntlie testsgzvem ahove thattmmlbslsq t otu,lbs./sq.1n. V I z mercapto ihiazfihn e7 unique (in'that'rthey my are greatly-activatedebyza omatioiacidseand anhm r d H In a Stock Stock Stock Stock' FF: HGG

' i 60 presence of an unsubstituted-aliphaticvmohocard .0

6R I I boxylicacid -o f-from- 10to-20 carbon atemsr-This---- 28 ,g: gggI activation r-is svery important in that itpermits 9 l 274 13750 7 175:775 3:150 the compounding of stocks that are very desirablecorfirneYcialli Thesestcfis gi'i e a'iastfliigh" modulus edge, and at'the 'sametime processfwlith it It has beenshownthat.2,-inercapto-thiazo1ihes I I a a a V are activated by small amounts ofan aromatic Not 'on1y"d.0% the viilcanizatesypy carboxylic acid or acidanhydride in the presence bu; ,iiw fitigfif OSSSS1NEXCHM4 of n aliph ticmonocarboxylic acid containing: modulus andjftnsill-,pihpezitiesthatltheyiia-lsbyllnc from -12020 carbonatoms. :Qther acidic a c- 7 posses'ssotlier.f rery desirable{physical,prdpertiesn celeratorsQhowever; suchas 2 -mercapto-benzo 7 Many stocks ccntaining.aniacceleratcix seat/meatthiaaole-r-are not ractivated byiavsimilar combina by another; substancesufien deteriorationw' fi tionpf acidsgbut are \usuallyfretardedinstead: 'physicakpi oper ties; due-rte theactivationr l hisf Thefollowing ztestsrshowthe;retardingactiontci-. is not true of thevulcanizates of our invention. these acid combinations onZ-me'rcapto-benzo- 7 Their resistance toward aging, for example is IStock RR ss Smoked sheets 100 100 Zinc xide l l0 Stearic acid 2 2 Sulfur3 3 Phenyl-beta-naphthylam 1 1' 2-mercapto-thiazo1ine 1 0.85 0.85-Salicylic acid 0. 5 Benzoic acid..- 0.

Table XI Stock RR stock ss Min. Temp. cured cured Orig- Tensile Qng-Tensile me] after me} after tensile aging tensile aging Vulcanizates,prepared according to our invention, also possess excellent resistancetoward Zinc salt of azoline azoline Aromatic Meta-toluicacid Para-toluicacid 7 Cetyl-benzoic acid I Dimethyl-benzoic acid Diethyl-benzoic acidBenzyl-benzoic acid deterioration by heat, tearing, abrasion and fiexecracking.

The foregoing test formulae are given for illustrative purposes only.variations within our invention will be readily apparent to thoseskilled in the art. Various compounding ingredients and fillers, otherthan those hereinbefore disclosed, may be employed and in varyingproportions. Also, other Z-mercapto-thiazoline accelerators maybeemployed in. place of those hereinbefore disclosed. .Some of suchother 2mercapto-thiazo1ine accelerators are as follows: I

4-ethyl-Z-mercapto-thiazoline fi-propyl-2-mercapto-thiazoline4,4-'dimethyl2-mercapto-thiazoline 5,5-dimethy1-2-mercapto-thiazoline4-methy1-4-ethyl-2-mercapto-thiazoline4-methyl-5-propyl-2-mercapto-thiazoline '4-isopropyl-5-propyl-2-mercapto-thiazoline' Many changes and Methyl-phenyl-benzoicacid Methyl-ethyl-benzoic acid Phenyl-ben'zoic acidAlpha-methyl-beta--naphthoic acid Anthracene carboxylic acidOrtho-toluic anhydride Cuminic anhydride Terephthalic acid Chlorobenzoicacid Aminobenzoic acid 2-hydroxy4: nethyl-benzoic acid 2 ethyl-4-methoxy-benzoic acid 4-methyl-phthalic acid v 2-chloro-4' isopropylbenzoic acid 2-methyl-4-amino-benzoic acid Alpha-hydroXy-betanaphthoic'acid Para-carboxwacetophenone j.

1 Para-carbethoxyibenzoici acid Beta-ethoxy alpha naphthoic acidPara-anisic acid anhydride I Ortho-chloro 'benzoic acid anhydride Also,unsubstituted aliphatic monocarboxylic.

acids of 10 to 26 carbon atoms,- other than those hereinbeforespecifically disclosed,ymay be employed in the combinations of ourinvention. Representativeof such other aliphatic acids are:

Palmitic acid Laurie acid Linoleic acid Margaric acid It will also beapparent that be employed as activators. Furthermore, mixtures of two ormorealiphatic carboxylic acids of our invention may be employed.

' It will be apparent that by our invention, we

'have converted Z-mercaptd-thiazolines from Cadmium salt of 4-methyl2-mercapto-thiazoline Zinc salt of 4-ethyl-2-mercapto-thiazoline Leadsalt of 5-propyl-2-mercaptothiazo1ine Y Cadmium salt of4,4-dimethyl-2-mercapto-thiazoline 1 Iron saltcf5,5dimethyl-2-mercapto-thiazoline Zinc salt of e-methyl--ethyl ilmercapto-thi- V azoline Cadmium salt of 4,4-dimethyl-5-propyl-2-mer-.

capto-thiazoline weak accelerators of no commercial value tov 1extremely active accelerators of very great commercial value. This hasbeen done'without ren-- dering the accelerators so active at the lower:

processing temperatures as to'make them unsafe for commercialutilization; By the combinations.

of our invention, fast, high modulus cures are obtained, with noreversion; and with greatv processing safety. The resulting vulcanizateshave exceedingly goodresistance toward tear,

abrasion and'flex crackin'g, as well as'excellent resistanceto'warddeterioration by heat or oxidation. We have renderedthe'Z-mercaptO-thiaZoe line accelerators at least as active as2-71erca'ptobenzothiazole at the normal vulcanizing" temper: atures and,at the same time, have obtained products having better properties;particularly v carboxylicac'ids, other than those hereinbeforespecifically disclosedfrnay be em-" ployed' in accordance with our'inventicnf Bepother ,aromatic icarboxylic Myristic acid mixtures of twoor more 2-mercapto-thiazolines may beemployed, as the accelerator; jMixt'ures' of two or'more aromatic carboxylic acids or our invention mayI I substituted aromatic dicarboxylic acids, sulfurfree aromaticmonocarboxylic acids containing one non-hydrocarbon substituent, andanhydrides of such acids, and then subjecting the rubber mix-tovulcanizing conditions.

12. Rubber, having incorporated therein prior to vulcanization, a smallproportion of a vulcanization accelerator of the group consisting of2-mercapto-thiazoline, C-alkyl Z-mercapto-thiazolines, C-hydroxyalkylZ-mercapto-thiazolines and metal salts of such 2-mercapto-thiazolines inwhich all of the valences of the metalsare satisfied by2-thio-thiazoline radicals, a small proportion of an unsubstitutedaliphatic monocarboxylic acid of from 10 to 20 carbon atoms and a smallproportion of a sulfur-free aromatic monocarboxylic acid containing notmore than one non-hydrocarbon group other than the carboxyl group.

13. Rubber, having incorporated therein prior to vulcanization, a smallproportion of a vulcanization accelerator of the group consisting ofZ-mercapto-thiazoline, C-alkyl Z-mercapto-thiazolines, C-hydroxyalkyl2-mercapto-thiazolines and metal salts of such Z-mercapto-thiazolines inwhich all of the valences of the metals are satisfied byZ-thio-thiazoline radicals, a, small proportion of an unsubstitutedaliphatic monocarboxylic acid of from 10 to 20 carbon atoms and a smallproportion of an aromatic mono- 'carboxylic acid which, except for thecarboxyl group, consists of carbon and hydrogen.

1%. Rubber, having incorporated therein prior to vulcanization, a smallproportion of a vulcanization accelerator of the group consisting of2nercaptc-thiazcline, C-allryl Z-mercapto-thiazolines, C-hydroxyalkylZ-mercapto-thiazolines and'metal salts of such 2-mercapto-thiazolines inwhich all of the valences of the metals are satisfied by2-thio-thiazoline radicals, a small proportion of an unsubstitutedaliphatic monocarboxylic acid of from 10 to 20 carbon atoms and a smallproportion of an aromatic monocarboxylic acid of the benzene'serieswhich, except for the carboxyl group, consists of carbon and hydrogen.

15. Rubber, having incorporated therein prior 'to vulcanization, a smallproportion of a vulcanization accelerator of the group consisting ofZ-mercapto-thiazoline, O-alkyl 2- mercapto-thi- 17. Rubber, havingincorporated therein prior to vulcanization, asmall proportion of2-mercapto-thiazoline, a small proportion of an un-.'

substituted aliphatic monocarboxylic "acidof from 10 to 20 carbonatomsand 'a small proportion of a sulfur-free aromatic monocarboxylicacid of the benzeneseries which contains not more than 1 non-hydrocarbongroup other than the carboxyl group. 7

18. Rubber, having incorporated therein prior to vulcanization, a smallproportion of Z-mercapto-thiazoline, a small proportion ofanunsubstituted aliphatic monocarboxylic acid of from 10 to 20 carbonatoms and asmall proportion of benzoic acid. I

19. The method ofvulcanizing rubber which comprises incorporating, intoa vulcanizable rubber mix, a small proportion of a vulcanizationaccelerator of the group consisting of 2-mercapto-thiazoline, C-allrylz-mercapto-thiazolines, C-hydroxyalkyl Z-mercapto-thiazOlines and metalsalts of such 2-mercapto-thiazolines in which all of the valences of themetals are sat isfied by Z-thio-thiazoline radicals, a small proportionof an unsubstituted aliphatic monocarboxylic acid of from 10 to 20carbon atoms and a small proportion of an aromatic monocarboxylic acidwhich, except for the carboxyl group, consists of carbon and hydrogen,andthen subjecting the rubber mix to vulcanizing conditions.

20. The method of vulcanizing rubber which comprises incorporating, intoa vulcanizable rubj ber mix, a small proportion of a vulcanizationaccelerator of the group consisting of Z-mercapto-thiazoline, C-alkyl2-mercapto-thiazolines, C-hydroxyalkyl Z-mercapto-thiazolines and metalsalts of such Z-niercapto-thiazolines in which all of the valences ofthe metals are satisiied by 2-thio-thiazoline radicals, a smallproportion of an unsubstituted aliphatic monocarboxylic acid'of'from 20to 20 carbon atoms and a azolines, C-hydroxyalkyl-2-'mercapto-thiazolines and metal salts of such2 mercapto-thiazolinesin which all of the valences of the metals are satisfiedbvB-thio-thiazoline radicals, a small proportion of an unsubstitutedaliphatic monocarboxylic acid of from 10 to 20 carbon atoms smallproportion of'an aromatic monocarboxylic acid of the benzeneseries-which, except for the carboxylgroup, consists of carbon andhydrogen, and then subjecting the rubber mix to vulcanizing conditions.

21. The method of vulcanizin'g rubber which comprises incorporating,-into a vulcanizable rubber mix, a small proportion of a vulcanizationaccelerator of the group consisting of 2 rnercapto-thiazoline, C-alkylZ-mercapto-thiazolines, C-hydroxyalkyl 2-mercapto-thiazolines and metalsalts of such Z-mercapto-thiazolines in Y which all of the valencesofthe metals are-sat isfied by 2-thio-thiazoline radicals, a smallproportion of an unsubstituted aliphatic monocar boxylic acid of from 10to 20 carbon atoms and a small proportion of benzoic acid, and then subjecting the rubber mix to vulcanizing conditions.

22. Rubber, having incorporated therein prior to vulcanization, a smallproportion of El-mercapto-thiazoline, a small proportion oi stearic acidand a small proportionof salicylic acid.

ARTHUR M. NEAL.

BERNARD M. STURGIS;

